Photosynthetic biogas upgrading to bio-methane: Boosting nutrient recovery via biomass productivity control

Abstract

Abstract. 16A pilot high rate algal pond (HRAP) interconnected to an external CO 2 −H 2 S absorption 17 column via settled broth recirculation was used to simultaneously treat a synthetic 18 digestate and to upgrade biogas to a bio-methane with sufficient quality to be injected 19 into natural gas grids. An innovative HRAP operational strategy with biomass 20 recirculation based on the control of algal-bacterial biomass productivity (2. Introduction.

Integral (VOCs, CO2, mercaptans and H2S) photosynthetic biogas upgrading using innovative biogas and digestate supply strategies

“…The photobioreactor configuration typically involves a High Rate Algal Pond (HRAP) interconnected to a biogas Absorption Column (AC) via recirculation of the algal cultivation broth. High CO 2 and H 2 S removal efficiencies (97-99% and 98-100%, respectively) have been reported using this process configuration, which allows recovering a biomethane complying with most European regulations for injection into natural gas grids [7].…”

“…Photosynthetic biogas upgrading is based on the simultaneous fixation of CO 2 by microalgae and oxidation of H 2 S to SO 4 2by sulfur-oxidizing bacteria using the O 2 photosynthetically produced. It is important to highlight that the environmental and economic feasibility of algal-bacterial photobioreactors devoted to biogas upgrading has been recently enhanced by using the digestate from the anaerobic digester as a water and nutrient source to support microbial growth [6,7]. The photobioreactor configuration typically involves a High Rate Algal Pond (HRAP) interconnected to a biogas Absorption Column (AC) via recirculation of the algal cultivation broth.…”

“…Microalgal photosynthesis in the HRAP is the main responsible for the dissolved oxygen that prevents complying with the strict O 2 levels imposed by biomethane standards [12][13][14]. In this regard, different strategies have been implemented with limited success to decrease the O 2 content in the upgraded biogas such as the use of co-current flow operation in the absorption column, a decrease in the recirculation liquid/biogas ratio (L/G) or the dosing of the digestate directly into the absorption column [7,[12][13][14]. Biogas supply during the dark period (when dissolved oxygen concentrations are low as a result of the null photosynthetic activity and active microalgal respiration) represents a promising and easy strategy to implement for minimizing oxygen stripping to biomethane.…”

Techno-Economic Analysis of Biogas Production from Microalgae through Anaerobic Digestion

“…The estimated cost of renewable natural gas is now reduced to 12.16 $/MMBtu and the electricity production cost from biogas is only 10.98 cents/kwh. Upgrading biogas by fixation of the CO 2 in biogas via photosynthesis by microalgae has been investigated with respect to CO 2 removal capability, biomass productivity and O 2 desorption minimization [16,[63][64][65][66][67]. Toledo-Cervantes et al [16] optimized the biogas upgrading process by studying the influence of the recycling liquid to biogas ratio.…”

“…Besides, no harsh pretreatment is necessary for algal biomass due to the negligible lignin content [14]. The algal biorefinery could be engineered to be resource efficient by recycling phosphorus and nitrogen nutrients in the digestate effluent and carbon dioxide from biogas upgrading processes for microalgae cultivation [13,14,16,17].…”